1. Field of the Invention
The present invention relates to an apparatus for gripping articles, and more particularly to an apparatus for selectively gripping and conveying articles.
2. Description of the Related Art
Conventional devices for gripping and conveying articles employ clamps with jaws which are held closed by mechanical actuators such as springs.
Conventional springs exert a force which is directly proportional to their displacement. Such a force is typically expressed by the equation F=kx, where x is the distance the spring is displaced, F is the force exerted at such displacement, and k is a constant, sometimes referred to as the spring constant. Due to this relationship, a spring which holds the jaws of a gripper in a closed position exerts a force which increases as the jaws are opened and which decreases as the jaws are closed. As a result, the force exerted while the jaws are in a closed position, gripping an article, is always less than the force exerted when the jaws are open or maintained in an open position for allowing an article to be inserted. This force to displacement relationship has the drawback of causing the gripper to exert its minimal force during gripping when a maximal force is desirable, and its maximal force when open, when a minimal force is desirable.
Gripper conveyors are used in repetitive high speed operations, such as in the mailroom of a newspaper printing plant. The springs in such gripper conveyors are highly subject to wear and mechanical fatigue which results in failures or improper performance. Maintaining and replacing such springs is costly and can result in devastating down-time for the entire gripping and conveying apparatus while the gripper conveyor is under maintenance or repair.
It is an object of the present invention to provide a simple and reliable gripper conveyor which will minimize maintenance, will not be subject to mechanical fatigue or failure, and will minimize the overall cost and down-time of the apparatus.
It is also an object to provide a gripper having a maximal force when gripping and a minimal force when open.
It is a further object to provide a gripper having a predictable closing force which will remain constant over the life of the gripper.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims.